1. Field of the Invention
The present invention relates to a solid-state image pickup apparatus, a method of manufacturing the same, and an image pickup apparatus.
2. Description of the Related Art
In response to the progress of the increase in number of pixels and the miniaturization of a pixel size, there has been proposed a technique of using a waveguide structure as a means for increasing a light collection efficiency of each pixel in a solid-state image sensor. In particular, in a CMOS image sensor, for forming a metal wiring on a light incident side of a photodiode, a waveguide structure, which guides incident light to a photodiode while confining the light and avoiding the metal wiring, is becoming a necessary technique.
A description will be given on an example of a solid-state image sensor having a waveguide structure in related art.
In a solid-state image sensor in related art, a photodiode that functions as a photoelectric converter is formed in an area separated by an element-separation insulating film or the like formed on a silicon substrate. On an upper surface of the silicon substrate adjacent to the photoelectric converter, a transfer gate electrode is disposed through a gate insulating film formed of a silicon oxide film and the like. Further, on the upper surface of the silicon substrate, a plurality of wiring layers made of a plurality of metal wirings are formed, and the metal wirings between the wiring layers are connected with each other through a through hole (bear hole) as appropriate.
On an uppermost wiring layer, a color filter is provided through a passivation film and a planarization film. On the color filter, a micro lens is disposed.
At a position corresponding to the micro lens and the photodiode, a waveguide that passes through the wiring layers is formed. The waveguide is formed by embedding a film having a little light-absorption property.
The waveguide optically connects an on-chip lens and a photodiode with each other and has a function of efficiently guiding light incident on the on-chip lens to the photodiode. Therefore, in the waveguide, a material having a refractive index higher than a material of an insulating film that forms the wiring layers is filled (see, for example, Japanese Patent Application Laid-open No. 2003-224249).
Along with the miniaturization, an absolute amount of incident light is reduced, and a light reception area of a photodiode that detects light is also reduced. If the degrees of the reduction are the same for colors (RGB), a spectral balance of the colors is the same as that of a previous generation, and a device design and a circuit design of a previous generation only have to be improved to a small extent.
When incident light beams have the same light amount, in a case of, for example, 1.75 μm□ cell and 1.1 μm□ cell, there are differences in quantum efficiency of the colors in the 1.1 μm□ cell along with the miniaturization. The light amounts of light (natural light) that enters the on-chip lens are the same regardless of the colors. Therefore, if light losses in components, such as the on-chip lens, the color filter, the planarization film, through which the incident light is guided are constant, signals that are output from the colors are proportional to the quantum efficiencies, with the result that the balance of the colors (spectral balance) may deteriorate.
There are some reports on a correction of the spectral balance.
The amounts of incident light are different between a pixel immediately below a position where the on-chip lens is disposed and a pixel distanced from the position. Therefore, a waveguide diameter of the distanced pixel is set to be thick (see, for example, Japanese Patent Application Laid-open No. 2006-190766).
In addition, in a system in which light is caused to be incident on a side of a photodiode of a solid-state image sensor, trenches are formed on a silicon substrate, depths of the trenches are set to be different for each color, and distances from bottom surfaces of the trenches to the photodiode are changed (see, for example, Japanese Patent Application Laid-open No. 2007-184603).